The lawsuit was filed under seal in U.S. District Court for the District of Delaware. A spokesman for Deerfield, Illinois-based Walgreens declined to comment Tuesday beyond confirming the lawsuit had been filed.

Theranos raised millions of dollars by pitching its technology as a cheaper, faster way to run blood tests. But the companies’ yearslong partnership unraveled after questions were raised about the reliability of Theranos‘ tests.

In June, Walgreens, the nation’s largest drugstore chain, severed ties with the company, closing all 40 of its Theranos Wellness Centers

In April, Theranos said it was under investigation or inspection by several government regulators, and in July its founder Elizabeth Holmes was banned from owning or running a medical lab for two years.

Theranos said Tuesday it plans to respond “vigorously” to what it said were unfounded allegations.

“Through its mishandling of our partnership and now this lawsuit, Walgreens has caused Theranos and its investors significant harm,” the company based in Palo Alto, California, said.